Along with that information, this request contains information about the previous revision of the package that GoCD knows about. Compare the "previous-revision" data of the example request shown below, with the response of the "Latest Revision" message to understand this.

Response - From the plugin

Expected response body: Just as with the "Lastest Revision" message, the plugin is expected to send a response, which contains information about the latest revision it can find of the package specified by the information in the request. The difference here, is that it needs to find a revision of the package which is greater than the one specified in the request. It can send an empty response ({}) to specify that it could not find a suitable package (for instance, if there has been no change, and the latest revision is still the one specified in the request).

Almost all the fields expected in this response are explained in this part of the user documentation. The extra map, named "data" in the response, can be filled with custom keys and values, which will be made available to the agent, as environment variables, when a job contains this plugin as a material.